Using Biofeedback to Combat the Effects of Muscle Inhibition

Let’s take a deeper look at how muscle inhibition occurs and why biofeedback can be a great solution for preventing the long-term effects of muscle inhibition.

If you haven’t checked out Mike Reinold’s “The Sports Physical Therapy Podcast” episode with Russ Paine, co-founder of mTrigger and Director of Rehabilitation at UT Physicians in Houston, Texas, I recommend you start there. This blog post will elaborate on the topics discussed by Russ and take a more in depth look at the research regarding muscle inhibition.

After an injury or surgery, muscle inhibition is one of the biggest concerns. Muscle inhibition is a reflexive response to an injury. It is characterized by an inability to recruit motor units of the muscles surrounding the injured joint.(1) As Russ points out in his discussion with Mike, muscle inhibition is often a result of three main culprits. Let’s break each of them down.

1. Immobilization
Immobilization leads to muscle inhibition. Multiple studies on both the upper and lower extremity have looked at the effects of bracing or casting on a muscles ability to function properly.(2,3) In a study by Clark and Mahato, after just 4-weeks of hand/wrist immobilization, strength decreased by 45%.(2)Furthermore, this period of immobilization caused corticospinal track inhibition – this track is primarily responsible for carrying motor information from the brain to the target muscle.(2) As a result, the cortical (brain) activity and voluntary muscle activation also decreased in this study by 13.5% and 23% accordingly.(2) Why is this important? The brain is highly involved in determining the strength/weakness of a muscle activation.(2) When there are high levels of cortical inhibition from immobilization, the muscle activation levels are greatly affected.(2)

In the lower extremity, a study comparing the effects of a hinge brace vs. a locked brace demonstrated a 50% loss of strength in 3 weeks. As a result, there was a 40% decrease in quadriceps EMG activity, something we can measure using mTrigger biofeedback. When looking at atrophy, there was only 11% atrophy of the quad muscle, thus the loss of strength has to be coming from a neuromuscular inhibition standpoint. Similar to what we discussed above. This is significant because it highlights the importance of regaining muscle activation and eliminating the effects of muscle inhibition in order to maximize strength gains down the road.

2. Swelling
Another main contributor to muscle inhibition is swelling.(4) In studies of heathy patients with healthy knees, 30cc of fluid injected in the knee is enough to decrease quad activation by 50%. This is an astonishing amount. The presence of swelling leads to a reflexive shutting down of the quad muscle in order to protect the knee from further damage.(5) This is a spinal inhibition of the femoral nerve, called the H-Reflex or Hoffmann’s Reflex. In essence, the H-reflex is a measure of motor neuron pool recruitment.(5) Swelling will lead to a decrease in motor neuron pool recruitment, which is seen as a decrease in neuromuscular recruitment and thereby voluntary muscle output measured though EMG.(5) Thus, following an injury the amplitude of the H-reflex is diminished indicating muscle inhibition.(5) Early exercise is often hindered by muscle inhibition when joint swelling exceeds a certain amount, limiting the patient’s ability to contract their muscle.(5) It is imperative this issue is address early on to prevent the catabolic effects of muscle inhibition moving forward as you try to build muscle back up.

3. Unloading
Unloading is the third culprit of muscle inhibition. Studies have shown being non-weight bearing for just 3 weeks leads to a 20% decrease in strength. Bed rest and periods of greater than 3 weeks lead to an even more significant decrease in muscle strength, cross sectional area, and power output.(6,7)

Clinical Pearls
So, what can we do to combat the effects of muscle inhibition? Russ Paine points out a few notable examples in his discussion with Mike Reinold.

If swelling is significant enough to cause muscle inhibition, some doctors will aspirate to minimize the cascade of events that occurs with chronic swelling and muscle inhibition. As patients start to weight bear and walk without an assistive device, do NOT allow them to limp or walk with a bent knee. Educating and teaching them proper walking mechanics is essential to getting the quad muscle to activating properly. Lastly, to help patients understand how to better activate their muscle (quadriceps or otherwise) mTrigger biofeedback is an excellent option.

Biofeedback can help improve muscle activation levels by providing visual feedback and thereby increasing cortical output with each exercise rep. Since the patient is able to see each repetition and has a goal to achieve, effort and cortical output are increased. This addresses the issue of muscle inhibition as well as the decreased cortical activity that comes along with it. Biofeedback requires more patient energy, focus, and work, which is ultimately what we want to help prevent/minimize the effects of inhibition.

Here are a few examples of exercises Russ mentions using the mTrigger biofeedback for to help teach muscle activation and proper gait.

Extension Lift Off – this is great for regaining full extension control post operatively

Single Leg Stance – this helps build confidence standing on a slightly bent knee for walking

Weight Shift to Single Leg Stance – this helps to emphasize the eccentric contraction of the quad during proper gait

High Step Walking Drill or Cone Walking – brings all the previous drills together to simulate gait

Importance of Proper Activation

We all know that you eventually need to load an injured joint or tissue. However, you do not want to load someone with poor movement patterns who lack neuromuscular control. The first 2-3 months of post operative care is when you are dealing with a neuromuscular deficit. Patients must re-establish the basic foundations of neuromuscular control in order to have the stability and strength necessary to load safely and successfully.

Summary
Muscle inhibition is a common issue after an injury or surgery that needs to be addressed immediately. Immobilization, swelling, and unloading all play a large role in the effects of muscle inhibition and loss of strength. mTrigger biofeedback is an excellent tool for helping patients to overcome the detrimental effects of muscle inhibition to promote better activation, less atrophy, better benefits, and faster results.

References
1. Glaviano NR, Bazett-Jones DM, Norte G. Gluteal muscle inhibition: Consequences of patellofemoral pain? Med Hypotheses. 2019;126:9-14. doi:10.1016/J.MEHY.2019.02.046
2. Clark BC, Mahato NK, Nakazawa M, Law TD, Thomas JS. The power of the mind: the cortex as a critical determinant of muscle strength/weakness. J Neurophysiol. 2014;112(12):3219. doi:10.1152/JN.00386.2014
3. Honkonen EE, Sillanpää PJ, Reito A, Mäenpää H, Mattila VM. A Randomized Controlled Trial Comparing a Patella-Stabilizing, Motion-Restricting Knee Brace Versus a Neoprene Nonhinged Knee Brace After a First-Time Traumatic Patellar Dislocation. Am J Sports Med. 2022;50(7):1867. doi:10.1177/03635465221090644
4. Sonnery-Cottet B, Saithna A, Quelard B, et al. Arthrogenic muscle inhibition after ACL reconstruction: a scoping review of the efficacy of interventions. Br J Sports Med. 2019;53(5):289-298. doi:10.1136/BJSPORTS-2017-098401
5. Hopkins JT, Ingersoll CD. Arthrogenic Muscle inhibition: A Limiting Factor in Joint Rehabilitation. J Sport Rehabil. 2000;9(2):135-159. doi:10.1123/JSR.9.2.135
6. Alkner BA, Tesch PA. Knee extensor and plantar flexor muscle size and function following 90 days of bed rest with or without resistance exercise. Eur J Appl Physiol. 2004;93(3):294-305. doi:10.1007/S00421-004-1172-8
7. Berg HE, Dudley GA, Haggmark T, Ohlsen H, Tesch PA. Effects of lower limb unloading on skeletal muscle mass and function in humans. J Appl Physiol (1985). 1991;70(4):1882-1885. doi:10.1152/JAPPL.1991.70.4.1882